Conventionally, a capacitive micro-machined ultrasound transducer (cMUT) has been manufactured through use of a semiconductor deposition technique. The cMUT is a very small diaphragm-like device which includes electrodes for converting a sonic vibration of an ultrasound signal to a modulated capacitance. The cMUT has a sacrificial layer between the electrodes. A DC bias and AC pulses are applied between the electrodes so as to modulate a capacitance charge to thereby generate an electric field, so that a diaphragm vibrates and thus an ultrasound wave is generated.
Further, there has been proposed a capacitive micro-machined ultrasound transducer (cMUT) whose capacitance is monitored by means of a capacitance regulator so as to adjust a bias charge thereof. The capacitance regulator measures a minute AC voltage stemming from charging or discharging at a diaphragm electrode to thereby measure the capacitance of the cMUT. Thus, the bias charge is produced and maintained (see, for example, “Patent Document 1”).    Patent Document 1: Japanese kohyo (PCT) Patent Publication No. 2004-503312